From: avatar (avatar@renegadeclothing.com.au)
Date: Sun Feb 02 2003 - 23:31:11 MST
Mike Lorrey wrote:
" No, the magnetosphere has little to do with atmospheric retention other than reducing the amount of radiation we receive."
No, there is a mixed bag of reports of the influence of factors such as gravity, life, chemical processes, impacts, vulcanic emission of gases and the solar wind.
Some authors claim it does have to do with atmosphereic retention in the case of Mars.
From http://www.physics.uc.edu/~sitko/Fall2002/10-TP_part3/tp3.html
"It appears that the very early Mars had a warmer, thicker, wetter atmosphere. The thicker atmosphere allowed liquid water to exist, at least for short periods of time, but maybe long stretches as well. The transition to a cooler, dryer climate occurred about 3.5 by ago. There are three current hypotheses for the source of this thinning:
. Formation of carbonates in surface rocks (although we do not have any proof for the presence of carbonates yet).
. Stripping by the solar wind.
. Erosion by impacts. Mars sits right at the edge of the asteroid belt"
From the Polish Mars society, in somewhat garbled translation argues that planetoid collision vapourised the planetary surface and gases failed to return to Mars due to the solar wind. http://chapters.marssociety.org/polska/mars_atmosphere.html
"Those gases in first time have been strongly heated (in this time they could be totally ionized), perhaps had been brought into open space, where, under fast cooling they could made gas clouds. However due to strong interaction of the solar wind and lack of strong planet magnetic field that could partially imprison them, they had moved outside present Mars orbit around the Sun."
Mike Lorrey writes:
" This is simply not true. Venus has little or no magnetosphere, yet it retains 92 times more atmosphere than we have, PLUS it is half thdistance to the sun, so it gets much more solar wind per square inch than we get."
Correct, though it does have an active volcanoe system.
:
And it doesn't answer the question of the influence of the magnetosphere on early stages of Venus's life:
['There are two ways to get a magnetic field and magnetosphere. An active field may be continually generated in a moving electrical conductor such as a churning liquid iron core. Apparently Venus lacks one. The other is a 'fossil' field frozen into rocks that solidified at some time in the past when there was an active field. Such a field would consist of lots of iron atoms all lined up with their magnetic north poles pointing the same direction (ditto their south magnetic poles in the opposite direction). But Venus is so hot from the surface all the way down that the atomic compasses are knocked out of alignment. The T where this occurs is called the Curie Temperature. So in the case of Venus, T > Tcurie, and any fossil magnetic field is lost.']
Mike Lorrey writes:
''Jovian planets are almost entirely atmosphere, yet solar wind does not strip them away either."
They are further away and have greater gravity.
Mike Lorrey writes:
"If life had not evolved here, the earth would have 50 times more atmosphere than it has now. Most of our original atmosphere is now
locked up as limestone rock. If the moon was not there to cause our active tectonics, life would have turned our atmosphere almost entirely
into rock as it once did to Mars. Instead, tectonics, as well as other biological processes recycles some of the limestone back to the
atmosphere. Enough CO2 is there to retain some solar energy at the surface, but not enough to block thermal radiation entirely."
Correct, but :'Carbonate rocks on Earth are formed in two ways: through a purely chemical process or via the action of living things. Both means require liquid water.
The chemical pathway involves carbon dioxide gases that dissolve in surface waters. CO2 molecules combine with water to form carbonate ions, which in turn join with calcium or magnesium to create a solid that settles onto the sea floor. Limestone (CaCO3) is an example of such a carbonate. Geologic changes can later expose such deposits, revealing beautiful features such as the white cliff faces pictured above.'
There is no water on Venus due to the heat from the Greenhouse effect. As there is no life either, the carbonate cannot form. Thus the heavy atmosphere on Venus. Mars may well have carbonate rocks as on Earth, which may have reduced its atmosphere in combination with the other factors mentioned at the start (including solar wind stripping) but in the absence of life.
So I guess we're both right and wrong.
I did forget about the carbonate stuff, but that isn't necessarily linked to life (e.g. Mars) and many authors cite other factors including the solar wind and the magnetosphere as being involved. One text http://physics.ucsd.edu/students/courses/fall2002/physics9/p9notes/Chapter10.pdf reads causes of Earth's atmosphere are:surface temperature and pressure, outgassing by vulcanism, loss of gasses into space, life, also: "Low gravity insufficient to retain early atmosphere" and "solar wind bombardment creates tenuous exosphere".
And just as a tease:
http://science.nasa.gov/newhome/headlines/ast08dec98_1.htm
Solar wind blows some of Earth's atmosphere into space
Unfortunately the main very recent reference book where I read about the early atmosphere is at the local library and unavailable.
Mike Lorrey wrote:
" I suggest those interested Fogg's textbook "Terraforming Planetary Environments" to become informed on the subject."
Thank you.
I would also suggest:
The Drexlerian Terraformation of Mars: A New Ark for Humanity
at: http://www.islandone.org/MMSG/9601-news.html#RTFToC53
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